Automatic, Hidden Unique ID

Hi, I am trying to make a product review database, and I want to have an ID field in the mysql database. So, how can I get php to generate a number automatically, hidden from the user, make sure it is right after the previous number, and make sure it hasn't been used, then save that as a variable. Thanks in advance. Thanks, Austin Carpenter _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com.